1. Field of the Invention
The present invention relates generally to an electronically controlled, high resolution light source, and more particularly, to a light-emitting edge structure having an uniform light emission filter.
2. Description of the Prior Art
Electroluminescence is a phenomena which occurs in certain materials from the passage of an electric current through the material. The electric current excites the electrons of the dopant in the light emitting material to higher energy levels. Emission of radiation thereafter occurs as the electrons emit or give up the excitation energy and fall back to lower energy levels. Such electrons can only have certain discrete energies. Therefore, the excitation energy is emitted or radiated at specific wavelengths depending on the particular material.
TFEL devices that employ the electroluminescence phenomena have been devised in the prior art. It is well known to utilize a TFEL device to provide an electronically controlled, high resolution light source. One arrangement which utilizes the TFEL device to provide the light source is a flat panel display system, such as disclosed in U.S. Patents to Asars et al (U.S. Pat. No. 4,110,664) and Luo et al (U.S. Pat. No. 4,006,383), assigned to the assignee of the present invention. In a TFEL flat panel display system, light emissions are produced substantially normal to a face of the device and so provide the light source at the device face. Another arrangement utilizing the TFEL device to provide the light source is a line array, or edge, emitter, such as disclosed in a U.S. Patent to Kun et al (U.S. Pat. No. 4,535,341), also assigned to the assignee of the present invention. In a TFEL edge emitter system, light emissions are produced substantially normal to an edge of the TFEL device and so provide the light source at the device edge. Edge emissions by the TFEL edge emitter system are typically 30 to 40 times brighter than the face emissions by the TFEL flat panel display system under approximately the same excitation conditions.
From the above discussion, it can be appreciated that the TFEL edge emitter system of the Kun et al patent potentially provides a high resolution light source promising orders of magnitude of improved performance over the TFEL flat panel face emitter system in terms of light emission brightness. For the TFEL edge emitter device to be able to reach its full commercial potential, it must be capable of use in applications, such as electrophotographic printing, which demand uniformity of light emission across the face of the device defined by the multiplicity of individual light-emitting faces of the pixels of the device.
However, using present manufacturing techniques, a large fraction of TFEL edge emitter devices are produced with deviations preventing them from meeting pixel-to-pixel light emission uniformity requirements for such applications. If only the small fraction of devices which meet light emission uniformity standards can be used in these application, then production costs will be substantially increased by this lower yield.
Consequently, a need exists for a way to compensate for the deviations in light emissions of the large fraction of TFEL edge emitter devices which fail to attain uniformity standards.